In recent years, in place of cathode-ray tubes (CRTs), thin, light flat panel displays have been increasingly used in a wide variety of fields. This is because personal information terminals such as personal computers and network accessible cellular phones have been popular at an accelerated pace as a result of development of information equipment and infrastructure for Internet-centered service systems. Such flat panel displays have also been used as household-use TVs instead of predominantly used conventional CRTs.
In particular, organic electroluminescence elements (organic EL elements) are devices which attract large attention in recent years. Organic EL elements emit light in response to electrical signals, and contain organic compounds as a light-emitting compound. Organic EL elements intrinsically have excellent display properties such as wide viewing angle, high contrast and high-speed response. Furthermore, they can realize thin, light, high-definition display devices from a small size to a large size. Thus, interest has focused on them as elements which will take the place of CRTs or LCDs.
There have been proposed various full-color display devices using organic electroluminescence elements. In one method for obtaining full-color images using three primary colors; i.e., red (R), green (G) and blue (B), color filters are used in combination with white organic ELs. In such full-color display devices, attempts have been made to form a top emission-type full-color display device and a bottom emission-type full-color display device. The top emission-type full-color display device contains a semi-transparent cathode as an upper electrode, and realizes high color reproducibility by extracting only light that has a specific wavelength outside the organic EL element through the multiple interference effect obtained between a light reflective film and the semi-transparent cathode. The bottom emission-type full-color display device contains a dielectric multilayer mirror under a semi-transparent or transparent lower electrode.
For example, among organic EL elements formed by laminating, in sequence, a first electrode made of a light reflective material, an organic layer containing an organic light-emitting layer, a light semi-transparent reflective layer and a second electrode made of a transparent material so that the organic layer becomes a resonance part, known is an organic EL element formed so that L (optical distance) in the following equation becomes the positive minimum value:(2L)/λ+Φ/(2π)=m 
where L denotes an optical distance (optical path length), λ denotes a peak wavelength of the spectrum of light intended to be extracted (or a wavelength of light intended to be extracted), m is an integer and Φ denotes a phase shift.
In full-color display devices employing such white organic EL in combination with color filters, by changing the thickness of an anode made of an inorganic material (e.g., indium tin oxide (ITO)), the optical path length L of each pixel is adjusted for extracting light of each color (see, for example, Patent Literatures 1 and 2).
However, when an inorganic material such as ITO is used in an optical path length-adjusting layer, the production process for a light-emitting display device becomes complicated, leading to elevation of the production cost and reduction of productivity.
For example, next will be described a conventional production process for a light-emitting display device containing an optical path length-adjusting layer.
First, reflective metals 2 are disposed on a substrate 1 so as to correspond red, green and blue pixels (see FIG. 12).
Next, an ITO film 10 is formed by, for example, sputtering or vapor deposition on the substrate on which the reflective metals 2 have been disposed (see FIG. 13).
Next, a resist composition containing a curable resin is applied on the ITO film 10 to form a resist layer 20 (see FIG. 14).
In the state where the reflective metals 2, the ITO film 10 and the resist layer 20 are disposed on the substrate 1, the resist layer 20 is covered with a mask 4 allowing it to be partially exposed to light, and the resist layer 20 in one pixel is selectively exposed to light L for curing the resin (see FIG. 15).
The exposed resist layer 20 is developed to remove the portions other than the exposed portions (see FIG. 16).
In this state, etching is performed using the residual resist layer 20 as a mask to remove the ITO film 10 except the ITO film 10 under the residual resist layer 20 (see FIG. 17).
Next, the resist layer 20 on the residual ITO film 10 is removed to establish a state where the reflective metal 2 and the ITO film 10 are disposed in one pixel (see FIG. 18).
Next, in order to form different optical path lengths, an ITO film 10 is formed again by, for example, sputtering or vapor deposition (see FIG. 19). As a result, in the one pixel region, the ITO film 10 is superposed on the ITO film 10 already formed on the reflective metal 2 in the previous step, thereby forming the difference in optical path length between the ITO film 10 in the one pixel region and that in the other pixel regions.
Next, a resist composition containing a curable resin is applied again on the ITO film 10 to form a resist layer 20 (see FIG. 20).
In the state where the reflective metals 2, the ITO film 10 and the resist layer 20 are disposed on the substrate 1, the resist layer is covered with a mask 4 allowing it to be partially exposed to light, and the one pixel region in which the ITO films 10 have been superposed each other and the adjacent pixel region thereto are exposed to light for curing the resin (see FIG. 21).
The exposed resist layer 20 is developed to remove the portions other than the exposed portions (see FIG. 22).
In this state, etching is performed using the residual resist layer 20 as a mask to remove the ITO film 10 except the ITO film 10 under the residual resist layer 20 (see FIG. 23).
Next, the resist layer 20 on the residual ITO film 10 is removed to form, on the substrate 1, a pixel region in which the reflective metal 2 and the superposed ITO films 10 have been formed and a pixel region in which the reflective metal 2 and the ITO film 10 have been formed (see FIG. 24).
Next, in order to further form different optical path lengths, an ITO film 10 is formed again by, for example, sputtering or vapor deposition (see FIG. 25). As a result, in two pixel regions in which the reflective metal 2 and the ITO film 10 have been formed, the ITO film 10 is superposed on the ITO film 10 already formed in the previous step, thereby forming the differences in optical path length by the thickness of the ITO film 10.
Next, a resist composition containing a curable resin is applied again on the ITO film 10 to form a resist layer 20 (see FIG. 26).
In the state where the reflective metals 2, the ITO film 10 and the resist layer 20 are disposed on the substrate 1, the resist layer is covered with a mask 4 allowing it to be partially exposed to light, and the resist layer 20 on each pixel is exposed to light for curing the resin (see FIG. 27).
The exposed resist layer 20 is developed to remove the portions other than the exposed portions (see FIG. 28).
In this state, etching is performed using the residual resist layer 20 as a mask to remove the ITO film 10 except the ITO film 10 under the residual resist layer 20 (see FIG. 29).
Next, the resist layer 20 on the residual ITO film 10 is removed to form optical path length-adjusting layers each being made of the ITO film 10 and having different thicknesses on each reflective metal 2 in each pixel region on the substrate 1 (see FIG. 30).
Next, in the state where the optical path length-adjusting layers each being made of the ITO film 10 and having different thicknesses are formed, an organic light-emitting layer 7 and a semi-transparent member 8 are formed in this order on each optical path length-adjusting layer, to thereby produce a light-emitting display device 400.
In the light-emitting display device 400, lights having been emitted from the organic light-emitting layers 7 are extracted from the semi-transparent member 8 as those having wavelengths of blue, green and red corresponding to the optical path lengths d1, d2 and d3 of the ITO films 10 with different thicknesses.
That is, lights having been emitted from the organic light-emitting layers 7 are resonated between the semi-transparent members 8 and the reflective metals 2 (i.e., through optical paths with lengths of d1, d2 and d3). As a result, lights having wavelengths of blue, green and red corresponding to the optical path lengths are intensified and can be extracted from the light-emitting display device 400 as blue, green and red lights.
As described above, the light-emitting display devices having the optical path length-adjusting layers realize highly definite full-color display by three primary colors of blue, green and red. But, when an inorganic material (e.g., ITO) is used for forming the optical path length-adjusting layer, the formation of the differences in optical path length requires formation of a resist layer, etching using the resist layer as a mask, and removal of the resist layer. In addition, these treatments must be performed every time when each optical path length difference is formed, leading to cumbersome production process.